1. Field of the Invention
The present invention relates in general to flaps such, for example, as control flaps of the type which are conventionally hingedly connected to the trailing edge of a stationary foil on a vessel--e.g., a hydrofoil vessel or the like--and, more particularly, to an improved hinge construction for pivotally connecting such a flap to the foil trailing edge and which permits hinged mounting of a single longitudinally extending flap along the entire extent of the foil trailing edge, or along any desired substantial portion thereof; yet, wherein the flap may be freely pivoted about its longitudinal hinged connection to the foil irrespective of deflection of the foil, flap and hinged connection due to fluid loading thereof. Stated differently, the invention pertains to a simple, yet highly effective, hinge connection which readily permits of pivotal movement of the longitudinally extending flap along the entire extent of the hinged connection thereof to the foil irrespective of foil/flap deflection and irrespective of the fact that such deflection results in establishment of a curvilinear foil trailing edge and, therefore, a curvilinear hinge line.
2. Background Art
It has long been recognized that trailing edge flaps for vessel control--particularly, for control of hydrofoil ships--are desirable and, indeed, often essential in order to permit reliable controlled maneuverability of the vessel; and, consequently, it has been a common practice to hingedly connect a plurality of such trailing edge flaps to the trailing edge of a foil with the leading edge of the flaps spaced from, but in close proximity to, the trailing edge of the foil. In such arrangements, it is also generally common for adjacent flaps to be interconnected in end-to-end fashion with each flap serving to drive at least one adjacent flap and with each flap (except for that flap or those flaps directly connected to external drive mechanisms) being driven by an adjacent flap. However, regardless of whether any given flap is functioning as a drive flap, a driven flap, or both, its leading edge is generally hingedly connected to the foil trailing edge at two points spaced apart in a span-wise direction; and, at those points of hinged connection, the flap leading edge and foil trailing edge will generally be deflected in like amounts and in unison by the pressure of the fluid through which the vessel is moving. Consequently, in these localized spaced regions of "hard" pivotal connection, it is theorectically possible and relatively simple to design mating edge contours which permit relative pivotal movement between the flap and foil without interference.
Unfortunately, however, in those regions of the mating flap leading edge and foil trailing edge which are located between the span-wise spaced hinge points of "hard" connection, dynamic conditions are such that in operation the pressure of the fluid medium through which the vessel is passing serves to cause significant deflection of both the foil (and its trailing edge) and the flap (and its leading edge). While the degree of deflection between such foil trailing edge and flap leading edge is substantially the same at the spaced "hard" points of hinged connection therebetween, in the "soft" regions intermediate such spaced "hard" points the degree of deflection between the two edges can be, and often is, significantly different.
Indeed, when dealing with a foil having a free tip that is not directly and positively connected to the vessel structure, the relative deflections of the flap leading edge and the foil trailing edge can be in opposite directions. For example, assuming that the vessel is a hydrofoil ship moving through the water and that the trailing edge control flap(s) is (are) shifted through a downward or negative angle of rotation for the purpose of improving lift and/or controlling maneuverability, those skilled in the art will appreciate that fluid pressure applied to the bottom surfaces of the flap/foil combination will cause the outer tip of the foil to be deflected upwardly to a greater extent than inboard regions thereof, thus producing a foil trailing edge contour that is slightly concave rather than linear. Considering any given flap having its leading edge hingedly connected to such concave foil trailing edge at two spaced span-wise points, it will be appreciated that at the two points of "hard" or hinged connection, the flap leading edge will move with the foil trailing edge and, hence, at those two points there is little, if any, tendency for interference between the flap and foil when the flap is pivoted. But, intermediate those two points, as well as inboard and/or outboard thereof, fluid pressure exerted by the water through which the vessel is moving will be applied directly to the undersurface of that flap, causing the flap and its leading edge to be deflected upwardly in the intermediate unrestrained region of the flap. That is, the central portion of the flap leading edge will be cambered or bowed upwardly so that the flap leading edge assumes a somewhat convex shape in the region of the concave foil trailing edge, thus causing interference between the two edges with resultant reduction in fatigue life thereof. A somewhat similar result occurs even when the two edges are deflected in the same direction since the two edges will tend to be deflected by different amounts, particularly at the mid-point of the flap leading edge.
The foregoing differential deflection problems, particularly in the "soft" hingedly connected regions of the flap/foil combination intermediate two span-wise spaced "hard" pivotal connections, have, for a long period of time, presented severe design problems for foil designers. Indeed, despite the long outstanding need for an effective flap/foil combination employing only a single flap, the foregoing problems have resulted in a "solution" wherein virtually all flap/foil combinations employ multiple side-by-side flaps, each of which is hingedly connected to the trailing foil edge at two span wise spaced "hard" pivotal connection points, together with all of the necessary and attendant drive interconnections and actuating mechanisms for adjacent flaps. Not only do such systems result in increased weight, cost and complexity, but, moreover, they present serious sealing problems with regard to prevention of bleed fluid passing through the gaps between the foil trailing edge and flap leading edge. And, moreover, despite the use of multiple side-by-side adjacent flaps each having a relatively short span-wise length and each hingedly connected to the foil trailing edge at two spaced span-wise "hard" pivotal connection points, the problems of differential deflection and interference between the mating flap and foil edges have persisted.
Prior to the advent of the present invention, various attempts have been made to solve the problems introduced by varying discontinuities at the junction of the flap leading edge and the foil trailing edge. One such attempt has involved the use of adjustable flap hinges; an approach involving cumbersome and expensive assembly procedures requiring the use of separate shims. Unfortunately, during routine periodic maintenance there is a distinct possibility that one or more of such shims will be removed and will not be replaced or, if replaced, will be improperly positioned, thereby promoting flap/foil interference, reducing fatigue life, increasing drag, and decreasing flap effectivity. Moreover, fatigue life of the foil is further severely reduced because such adjustable hinge connections introduce undesired stress concentrations at localized points.
A second approach that has been employed, but which has been found to be entirely unsatisfactory, has been that of simply providing a sufficiently large gap or discontinuity at the hinged connections and, therefore, along the juncture of the flap leading edge and foil trailing edge in the span-wise spaces intermediate, inboard of, and outboard of the "hard" hinged connections, so that flap/foil interference is precluded even under those operating conditions when the edges are subjected to maximum differential deflection. Although this approach has eliminated the problems of reduced fatigue life, cost, and difficulties in assembly procedures, at the same time the excessively large discontinuities or gaps have further increased drag and reduced flap effectivity.
Exemplary of the prior art approaches are those disclosures found in Cone, U.S. Pat. No. 2,152,029; Roeseler et al., U.S. Pat. No. 4,213,587; Feifel, U.S. Pat. No. 4,305,177; Warner et al., U.S. Pat. No. 4,335,671. Thus, each of the foregoing patents is illustrative of prior art approaches employing segmented flaps. In the Roeseler et al, Feifel and Warner et al patents, the adjacent flap segments are each hingedly connected to the foil trailing edge at two span-wise spaced "hard" connection points with each such "hard" connection being shared by two adjacent flaps; and, with the flaps being interconnected along their adjacent edges for mutual drive purposes. Nevertheless, as recognized in the Warner et al patent, the points of "soft" hinged connection between adjacent points of "hard" connection still produce flap/foil interference when the flap is actuated; and, to solve that problem, the patentees provide for a special flap leading edge contour in which the flap leading edge is "drifted" back relative to the axis of flap rotation so as to increase the gap between the flap/foil combination in the " soft" regions of hinged connection.
Efforts to provide arrangements enabling the use of a single flap are disclosed in Sutton et al., U.S. Pat. No. 3,140,066 and Clark, British Pat. No. 734,959. Thus, in the Clark construction the flap is coupled to the foil trailing edge by means of a plurality of circular sliding blocks which are capable of relative fore/aft movement with respect to the foil trailing edge. However, such sliding devices are located at span-wise discrete locations and provide poor support, particularly in the case of hydrofoils which are subjected to high load conditions. The construction inherently produces concentrated load points and requires complex close tolerance fabrication operations. Similarly, in the Sutton et al patent, it is proposed that a plurality of span-wise "hard" hinged connections permit of relative fore/aft movement between the flap and foil. Again, the device is subject to concentrated loads, requires stress risers in the flap and foil structures, and fails to provide for proper sealing between the upper and lower aerodynamic control surfaces.